Technical Field
The present invention relates to a method for filling a container with a fill product using a proportional valve, and in particular to filling a container with a beverage.
Related Art
In order to fill containers with fill products in beverage filling plants, various possibilities are known for determining the volume flow of the fill product into the container that is to be filled, in order to specify the end of the filling process or the switch-off time point.
For example, it is known to measure the weight of the container by means of a weighing cell, and to determine the volume flowing into the container by means of the change in weight that occurs in the container during the filling process, in order in this manner to specify a switch-off time point.
It is further known to determine the volume of fill product flowing into the container by means of a volume flow meter, for example an inductive volume flow meter. This volume flow meter is typically disposed above the filler valve, and measures the volume flowing into the container during the filling process. Accordingly, the filling process can be ended when a predetermined fill volume is reached.
The known methods for ending the filling process are accordingly control methods, in which a measuring element is provided, for example a flow meter or a weighing cell, by means of which the filling process is controlled.
Filler valves, as well as the fill product flowing through the filler valves, have a certain intrinsic inertia, with the result that when the command to close is issued at the end of the filling process, the flow of fill product does not cease immediately, but only after a certain lag. In order to enable a container to be filled with exactly a specified fill volume, it is necessary to determine this lag and correspondingly advance the time of issue of the command to close, such that the correct fill volume is achieved in the container with the lag taken into account.
For this purpose it is known to use the measuring element also to measure the lag after the filler valve is switched off, for example using the weighing cell or the volume flow sensor, and then to advance the switch-off time point of the filling process correspondingly on the basis of the knowledge of the lag volume. This is therefore a control process in which a measuring element is provided for determining the lag volume, and in which the switch-off time point, at which the filler valve is closed, is corrected to take account of this lag volume.
In order to be able to control in a stepless manner the fill volume flowing into the container, and thereby to be able to trace volume flow curves that are optimized according to the fill product, filler valves are known that are designed as proportional valves, and which thus enable a substantially stepless control of the volume flow. Such a proportional valve is usually driven by a stepper motor, such that it can reach a desired open position in a reliable and reproducible manner. Due to the fact that the proportional valve is driven by the stepper motor, however, the closing process towards the end of the filling process is significantly longer than in the case of a conventional switching valve. The closure times that can be achieved are longer by a factor of approximately five. Correspondingly, the lag volume which flows through the proportional valve from the time the command is given until the proportional valve is fully closed is significantly greater than with a conventional switching valve.
It is also known when such a proportional valve is used to determine the lag volume during every filling process, for example by means of a volume flow sensor or a weighing cell, and correspondingly to determine the optimized switch-off time point by means of a control process. The volume flow during the lag varies, however, according to both the viscosity of the fill product and the differential pressure, i.e., according to the fill level of the fill product in the supply vessel, with the result that the control process must be repeated for every filling process, and the outcomes of the filling process vary according to the speed of the control process.